Automotive engines often have an air pump that supplies air to the engine exhaust system. The air supports combustion of hydrocarbons and carbon monoxide in the exhaust system to minimize emission of those compounds into the atmosphere.
In the past, such air pumps generally have had a mechanical drive from the engine and accordingly consumed power from the engine during all operating modes. In many applications, however, air is required to support combustion in the exhaust system only during the initial period of engine warm-up. Thus in those applications, the air pump has undesirably consumed engine power after the initial period of engine warm-up.